This invention relates to an apparatus and method for blow molding an article from a parison.
According to one type of conventional blow molding technique, a blow needle is employed to puncture a parison for the purpose of extending the needle into the parison and introducing air into the parison from the end of the needle to thereby inflate the parison and force its walls against the surface of a mold to produce a molded article. One significant problem which arises in such blow molding techniques is the tendency of air within the parison to leak therefrom through gaps between the parison wall and the blow needle. Such undesirable gaps frequently arise from the puncturing of the parison wall, and are then further increased in size by air pressure within the parison and the forces of gravity, particularly with heavy parison walls, which tend to pull the parison wall away from the blow needle. Air which leaks from within the parison through such gaps tends to flow between the mold surfaces and the parison, and results in the loss of air pressure within the parison which causes poor definition and warpage of the finished molded article. Leakage of air from the parison can also cause poor cooling of the parison and consequent low production rates.